Attention promotes episodic encoding by stabilizing hippocampal representations

Significance Why does the brain store memories of some things but not others? At a cognitive level, attention provides an explanation: What aspects of an experience we focus on determines what information is perceived and available for encoding. But the mechanism of how attention alters memory formation at the neural level is unknown. With high-resolution neuroimaging, we show that attention alters the state of a key brain structure for memory, the hippocampus, and that the extent to which this occurs predicts whether the attended information gets stored in memory. The dependence of hippocampal encoding on attentional states reveals the broad involvement of the hippocampus in multiple cognitive processes, and highlights that the workings of the hippocampus are under our control. Attention influences what is later remembered, but little is known about how this occurs in the brain. We hypothesized that behavioral goals modulate the attentional state of the hippocampus to prioritize goal-relevant aspects of experience for encoding. Participants viewed rooms with paintings, attending to room layouts or painting styles on different trials during high-resolution functional MRI. We identified template activity patterns in each hippocampal subfield that corresponded to the attentional state induced by each task. Participants then incidentally encoded new rooms with art while attending to the layout or painting style, and memory was subsequently tested. We found that when task-relevant information was better remembered, the hippocampus was more likely to have been in the correct attentional state during encoding. This effect was specific to the hippocampus, and not found in medial temporal lobe cortex, category-selective areas of the visual system, or elsewhere in the brain. These findings provide mechanistic insight into how attention transforms percepts into memories.